This invention relates to sandwich panels and to methods of fabricating sandwich panels.
As referrred to herein, the term "sandwich panel" means a composite panel having a top skin and a bottom skin structurally connected by an interposed core, the core being partially hollow, wherein the sandwich panel has high strength and low weight.
In general, prior sandwich panels have incorporated preformed cores to which the top and bottom skins are attached. Examples of prior sandwich panels range from corrugated boxboard for packaging to honeycomb panels for aircraft. Corrugated boxboard is not very strong; it compresses easily and has a tendency to bend along the lines of corrugation. Thus, there is a need for better boxboard, but it must be producible at low cost in order to be a viable replacement for present corrugated boxboard.
The present honeycomb panels used in fabrication of aircraft or other high strength, low weight structures also have disadvantages. The usual method of manufacturing honeycomb panels is to prepare a prefabricated hexagonal cell core. In the fabrication of stainless steel honeycomb panels, this is accomplished by strip welding sheets of metal at spaced apart intervals and expanding the sheets of metal to define hexagonal cells. The resultant hexagonal cell core structure is sliced to the desired core thickness and glued or welded between top and bottom skins to form the final sandwich panel. This method of manufacturing sandwich panels is expensive, for instance, it is too expensive to utilize in making better boxboard for general use. The hexagonal cell core also has "grain", i.e. it bends more easily in one direction than in others, and this is undesirable. Although it is preferable to have a multidirectional hex structure for the core of sandwich panels, a preformed multidirectional hex structure cannot be made except by molding plastic or the like with the desired multidirectional hex orientation. Further, it is difficult to fabricate sandwich panels having simple curves, and exceedingly difficult to fabricate sandwich panels having compound curves with sharp radii of curvature.
Accordingly, there is a need for sandwich panels which can be manufactured less expensively, and yet have the desired properties of high strength and low weight associated with prior art sandwich panels. There is also a need for methods of fabricating such improved sandwich panels.